The invention relates to blades for turbo machines and, in particular, to leading edge treatments to increase blade tolerance to erosion.
Water is sprayed in a compressor to wash the blades and improve performance of the compressor. Water washes are used to clean the compressor flow path especially in large industrial gas turbines, such as those used by utilities to generate electricity. Water is sprayed directly into the inlet to the compressor uniformly across the flow path. The rotating first stage blades of the compressor tend to erode at their leading edges of the airfoil especially at the root of the airfoil, which is where the blade airfoil attaches to the blade platform.
Water spray is a source of erosion to the leading edges of compressor blades and especially to first stage compressor blades. Other sources of erosion include debris and moisture in the intake air that erode the leading edge of a compressor blade and combustion products that erode the trailing edge of a turbine blade (also known as a bucket). Erosion can pit, crevice or otherwise deform the edge surfaces of a compressor blade and turbine bucket. As erosion continues, the population of pits and crevices increases and they deepen into the airfoil surface of the blade.
In addition, a blade is under tremendous stress due to centrifugal forces and forced vibration due to the airflow and the turbo machine. These stresses tear at the erosion pits and crevices and potentially lead to a high cycle fatigue (HCF) crack in the blade. Once a crack develops, the high steady state stresses due to the centrifugal forces that act on a blade and the normal vibratory stresses on the blade can cause the crack to propagate through the blade and eventually cause the blade to fail.